1. Field of the Invention
This invention relates to a process for stabilizing wet process phosphoric acid. In particular, this invention relates to a process for stabilizing wet process phosphoric acid by enhancing the rate of post-precipitation of impurities.
2. Description of the Prior Art
Wet process phosphoric acid is obtained by acidulating phosphate rock with a mineral acid, such as sulfuric acid. Wet process phosphoric acid typically contains numerous suspended and dissolved impurities, principally gypsum, but also including iron, aluminium and magnesium compounds. While, most of these impurities are separated in what are now conventional purification and concentration steps for making wet process acid, and thus need not be described in any detail, a significant amount of these impurities remain in the concentrated commercial grade acid.
The wet process acid usually is concentrated to about 50-60% P.sub.2 O.sub.5 for shipment. This concentrated product generally is referred to as merchant acid. During subsequent storage and shipment of the concentrated merchant acid, residual impurities in the acid form a precipitate or sludge which separates slowly over time from the concentrated acid causing numerous problems. This sludge, known in the art as post-precipitate, is difficult and costly to remove from the concentrated acid.
While various procedures have been proposed in the prior art for remedying the problem of post-precipitation, they all suffer from a variety of infirmities. Thus, a continuing need exists in this art for a simple technique for reducing the post-precipitation of impurities from concentrated wet process phosphoric acid.